Non-ablative, state changeable, projected energy beam data storage system, for example optical data storage systems, record information in a state changeable material that is switchable between at least two detectable states by the application of projected beam energy thereto. The projected beam energy may be optical energy, particle beam energy, or the like.
The state changeable optical data storage material is present in an optical data storage device having a structure such that the optical data storage material is supported by a substrate or substrates and encapsulated in encapsulants. The various layers of encapsulants may include sealing layers, anti-ablation materials and layers, thermal insulating materials and layers, anti-reflection layers, and reflective layers. Various layers may perform more than one of these functions. The thicknesses of these layers, including the layer of state changeable data storage material, are optimized whereby to minimize the energy necessary for state change while retaining the high contrast ratio, high carrier to noise ratio, and high stability of the state changeable data storage material.
The state changeable material is a material capable of being switched from one detectable state to another detectable state by the application of projected beam energy thereto. State changeable materials are such that the detectable states may differ in their morphology, surface topography, relative degree of order, relative degree of disorder, nature of order or disorder, electrical properties, and/or optical properties. Moreover, the changes in properties must be detectable by, for example, the electrical conductivity, electrical resistivity, optical tranmissivity, optical absorption, optical reflectivity, index of refracting, or a combination thereof.
The data storage material is typically deposited as a disordered material and formed or initialized to a solid system having (1) relatively reproducible properties in the relatively ordered or even crystalline state, and (2) relatively reproducible properties in the relatively disordered or even amorphous state. Moreover, there should be a relatively high degree of history invariant discrimination between these states for a high number of write-erase cycles, i.e. for a relatively high number of vitrify-crystallize cycles.
Tellurium based materials have been utilized as phase changeable memory materials. This effect is described, for example, in J. Feinleib, J. deNeufville, S. C. Moss, and S. R. Ovshinsky, "Rapid Reversible Light-Induced Crystallination of Amorphous Semiconductors", Appl. Phys. Lett., Vol. 18(6), pages 254-257 (Mar. 15, 1971), and in U.S. Pat. No. 3,530,441 to S. R. Ovshinsky for Method and Apparatus For Storing And Retrieving Of Information. A recent description of tellurium-germanium-tin systems, without oxygen, is in M. Chen, K. A. Rubin, V. Marrello, U. G. Gerber, and V. B. Jipson, "Reversibility And Stability of Tellurium Alloys For Optical Data Storage," Appl. Phys. Lett., Vol. 46(8), pages 734-736 (Apr. 15, 1985). A recent description of tellurium-germanium-tin systems with oxygen is in M. Takanaga, N. Yamada, S. Ohara, K. Nishiuchi, M. Nagashima, T. Kashibara, S. Nakamura, and T. Yamashita, "New Optical Erasable Medium Using Tellurium Suboxide Thin Film", Proceedings, SPIE Conference on Optical Data Storage, Arlington, Va., 1983, pages 173-177.
Tellurium based state changeable materials have heretofore been characterized as single phase or multiphase systems (1) where the ordering phenomena include nucleation and growth processes (both homogeneous and hetrogeneous) to convert a system of disordered materials to a system of ordered and disordered materials, and (2) where the vitrification phenomenon includes melting and rapid solidification of the phase changeable material to form a system of disordered and ordered components from a system largely of disordered components. The above phase changes and separations occur over relatively small distances with intimate interlocking phases and gross structural discrimination.
In chalcogen type memory materials the measures of performance include (1) the contrast ratio, that is, the difference in reflectivities of the states divided by the sums of the reflectivities of the states, and (2) the carrier to noise ratios of both (a) the "written" and (b) the "erased" states. The failure mode of the memory material is evidenced by the deterioration in the measures of performance with respect to the number of cycles. That is, failure may be evidenced by (1) a reduction in contrast ratio with increasing cycles, or by (2) a reduction in the written carrier to noise ratio or an increase in the erased carrier to noise ratio. The exact mechanism for these failures have not heretofore been fully understood.